1. Field of the Invention
The invention relates generally to an integral speed reduction and wheel mounting unit for a motor vehicle and, more particularly, to an integral speed reduction and wheel mounting unit including an axle pivot member, spaced annular bearings located on the axle pivot member and an axle housing mounted on the annular bearings so that either the axle pivot member or the axle housing can function as a driven hub.
2. Description of Related Prior Art
The prior art discloses many different arrangements of such units. For example, German Patent No. DE-OS 28 43 597 discloses a wheel bearing unit designed as a two-row annular bearing wherein the external bearing surfaces of the two rows of bearings are cast on the inside of the axle housing which is a stationary hub bracket and, therefore, also has a fastening flange cast thereon. This design provides a system having a relatively small number of component parts. However, the disadvantage of a wheel bearing unit according to this prior art design is that the torque amplification between the drive engine of the vehicle and the driven vehicle wheels takes place upstream of the wheel bearing unit and a separate transmission is required which significantly increases the amount of space required and the weight of the vehicle. Additionally, a wheel bearing unit according to this prior art design requires cost-intensive fabrication and installation operations. Moreover, the design requires the transmittal of large torques to the wheel by a transmission having complex and expensive shafts with universal joints.
U.S. Pat. No. 4,275,616 entitled "Hydraulic Wheel Drive" discloses a gear train inside a wheel drive on a machine tool. The design is completely different from the wheel bearing units of the prior art which are used in the mass production of motor vehicles. The axle housing is designed as a hub and is rotationally mounted on the axle pivot member which serves as the hub bracket. The end surface of the axle pivot member adjacent to the wheel is the stationary plate of a planetary gear train. The planetary gear train is an axial extension of the hub bracket which makes the arrangement quite long which requires a significant amount of space. Moreover, if the motor vehicle is equipped with dual tires a severe load is placed on the roller bearings since the lever arm on which the wheel forces are exerted is very long.
U.S. Pat. No. 4,896,740 entitled "Wheel Bearing Support" discloses a wheel head for the live front axle of a farm tractor in which the axle housing is rotationally mounted on a stationary axle pivot member. The inside of the rotating axle housing provides a ring gear of a step-down transmission between spaced roller bearings. The ring gear and thus the axle housing or hub are connected by an eccentrically located drive shaft and by two intermediate wheels mounted on the stationary axle pivot member or hub bracket. This design also occupies a great deal of space and, additionally, is restricted to use in a system in which the axle pivot member is stationary and the axle housing rotates.